1. Field Investigations: How to Investigate an Outbreak
Quarantine Epidemiology and Surveillance Team
Quarantine and Border Health Security Branch/DGMQ/NCEZID
Centers for Disease Control and Prevention

2. Why Initiate an Investigation?
Characterize the problem
Rational basis for control and prevention
Research--answer scientific questions
Training of epidemiologists
Political / legal concerns
Program considerations

3. Guidelines for Epidemiologic Field Investigations
Prepare for field work
Verify diagnosis
Confirm epidemic
Identify and count cases
create case definition
develop line listing
Tabulate and orient data: time, place, and person
Take immediate control measures
Formulate and test hypothesis
Plan additional studies
Implement and evaluate control measures
Initiate surveillance
Communicate findings

4. Guidelines for Epidemiologic Field Investigations
Prepare for field work
Verify diagnosis
Confirm epidemic
Identify and count cases
create case definition
develop line listing
Tabulate and orient data: time, place, and person
Take immediate control measures
Formulate and test hypothesis
Plan additional studies
Implement and evaluate control measures
Initiate surveillance
Communicate findings

5. Verify Diagnosis Goal is to rule out: misdiagnosis laboratory error
Examine case-patient(s)
Review medical records
Confirm laboratory testing

6. Confirm Epidemic Establish baseline
Compare magnitude of present problem with baseline

7. Incidence of Kaposi's Sarcoma (KS), Pneumocystis carinii Pneumonia (PCP), and Other Opportunistic Infections in the U.S.,
1979
1980
1981

8. Identify and Count Cases
Goals:
identify maximum number of cases
exclude noncases
Consider spectrum of manifestations
Develop case definition
set of conditions
specific time period
specific location

9. Case Definitions Problem: Case: Confirmed case: Presumptive case:
Outbreak of legionnaires disease in persons who had visited Bloomington Indiana
Case:
An illness characterized by pneumonia or fever and cough in a person who had been in Bloomington, Indiana, in the two weeks prior to onset of illness
Confirmed case:
Either 1) LDB in lung tissue by direct FA technique, or 2) a 4-fold rise in titer of serum antibodies by the IFA technique
Presumptive case:
A single convalescent IFA specimen with titer of 1:256 to LDB

10. Identify and Count Cases
Conduct systematic search
Use multiple sources
Construct a line list

11. Orient Data
Time
Place
Person

12. Descriptive Epidemiologic Process}
WHEN were they affected?
WHERE were they affected?
WHO was affected?
HOW
and
WHY?

13. Ordering Key Events Onset of manifestations in cases and contacts
Period of exposure to causal agents or risk factors
When treatments given
When control measures implemented
Potentially related events or unusual circumstances

14. Time Epidemic curve: # of cases by time of onset
Configuration permits inferences
agent known: use incubation period to look back at exposure
agent unknown, but common event likely: postulate agent by determining the incubation period
Construct relative to specific sites or groups
Time intervals: less than known/suspected incubation periods

15. Correlation of hospital course of hepatitis A source patient with laboratory values and onset of illness in secondary cases – GA, September 1- October 31, 1980 1 2 3 5 9 13 17 21 25 29 7 11 15 19 23 27 31 4 6 8 10
500
1000
1500
2000
2500
September
October
Cholecystectomy
Onset of diarrhea
and vomiting
Jaundice noted
Hepatitis A noted
Cases
Bilirubin (mg %)
SGOT (mu/ml)
SGOT
Bilirubin
(Source: Goodman et. al 1982.)
et al.

16. Salmonellosis in passengers on a flight from London to the United States, by time of onset, March 13-14, 1984
Supper 4
a.m.
Snack 10 2 1
p.m.
Flight time
12PM
12AM
March 13
March 14
Onset (3-hour periods)

17. Cases of Influenza-like Illness Among Residents of a Nursing Home in Rural Minnesota. April 24-May 21, 1979
April
May

18. Cases of Influenza-like Illness Among Residents of a Nursing Home in Rural Minnesota. April 24-May 21, 1979

19. Legionnaires' Disease by date of onset, Philadelphia, July 1-August 18, 1976
American Legion
Convention
August

20. Distribution of Hepatitis A Cases By Month of Onset

21. VHF Deaths, Bandudu Province, Zaire. March - April 1995
Surgery and
Hospital Outbreak
*Note: 7 deaths with unknown date of onset

22. Place Orient to: Spot map: specific residence and/or exposure
place of residence
place of occupation
activity sites
Spot map: specific residence and/or exposure
within buildings
city blocks or neighborhoods
county or state level

23. Distribution of cholera cases and implicated water well Golden Square area of London, Aug--Sept, 1848
WORK
HOUSE
CARNABY STREET
MARSHALL STREET
REGENT STREET
GREAT PULTENEY STREET
BERWICK STREET
BROAD STREET
SILVER STREET X
POLAND STREET
GOLDEN
SQUARE N S E W
PUMP B
PUMP
PUMP C
PUMP A

24. Brewery

25. Culture-positive cases of shigellosis, by sites along the Mississippi River where each case swam within three days of onset of illness --- Dubuque, Iowa, September, 1974
Sewage Treatment Plant
Cases
Water contact site is beyond
the margin of the map

26. Minnesota South Dakota Iowa
Incidence per 10,000 persons of thyrotoxicosis by county. Minnesota, South Dakota, and Iowa, Feb Aug 1985
Minnesota
Lac Qui Parle
Yellow Medicine 1 5 1
Lincoln
Lyon
Redwood
South
Dakota
Brown 10 5
Pipestone
Murray
Cottonwood 2 40 9
Sioux Falls
Minnehaha
Rock
Nobles
Jackson
Valley Springs
Luverne 1 2
Lyon
Osceola
Iowa

27. Sverdlovsk, USSR (April 1979)
Anthrax Outbreak
April-May 1979

29. Person Thoroughly describe the case group
Identify factors shared in common by cases
Obtain denominators to derive rates
Compare groups

30. Formulate and Test Hypothesis
Goal: explain the problem
Use comparison group(s)
case-control study
cohort study
Consider causation

31. Implement Control Measures
Eliminate/treat source
Cohorting
Prevent further exposures
Protect at-risk population

32. Communicate Findings Purposes: formally convey recommendations
institutional requirements
record for future reference
rapid dissemination
share experience
Forms:
preliminary written report
final report
public health bulletin
journal article
abstract
meeting presentation